This invention is directed to an axle assembly for a vehicle and, more specifically, to a trailer axle assembly including fluid powered brake mechanisms and a brake fluid relay valve mounted directly to the axle as a unitary assembly. The invention is particularly applicable to a trailer axle utilizing an anti-skid brake control system and provides a mounting plate for securing the brake control or relay valve directly to the axle.
Anti-skid brake control systems are now required on many commercial vehicles in the United States and are being adopted in other countries in the interest of traffic safety. One such system is disclosed in U.S. Pat. No. 3,790,227 which issued to L. C. Dozier on Feb. 5, 1974. A brake control valve which may be employed in such a system is disclosed in U.S. Pat. No. 3,740,105 which issued to A. B. Holmes on June 19, 1973.
Relay valves are used on trucks and trailers to supply air from a source such as an air reservoir to the vehicle brakes when the vehicle operator depresses the brake pedal. The relay or control valve in an anti-skid brake system operates in direct response to depression of the brake pedal, but also includes means for modulating the vehicle operator directed application of the brake fluid pressure in the event a wheel or wheel set decelerates at such a rate as to indicate an incipient skid condition. In such a system the angular velocity of the wheels at opposite ends of an axle is monitored by sensors which emit electrical signals indicative of the angular velocity of each wheel or wheel set and the signals are compared by electrical means. If an incipient skid condition is detected, the electrical means actuates an override device to modulate the vehicle operator directed application of brake fluid pressure until such time that the incipient skid condition no longer exists or the vehicle is brought to a stop. In the control valve disclosed in the aforesaid patent, the override device is a solenoid which operates a valve to modulate the application of control pressure to the relay valve. The solenoid is actuated by a electronic computer which is mounted in the relay or control valve body and electrically connected to the wheel speed sensors and the solenoid.
Relay or control valves are usually mounted directly to the chassis or frame of a truck or trailer where they are protected from road shock and axle vibration by the vehicle suspension. With the advent of safety regulations requiring anti-skid brake control systems for each axle of a vehicle, it has become apparent that certain advantages could be obtained from the use of a self-contained anti-wheel lock axle assembly requiring only an electrical connection to a power source and fluid pressure connections, usually air lines, to a source of fluid pressure and to the operator actuated brake pedal. Such an axle assembly and the advantages obtained thereby are disclosed in application Serial No. 550,096 filed on February 15, 1975, now U.S. Pat. No. 3,936,096 which is assigned to the assignee of the present invention.
Early attempts to mount a relay valve directly to an axle were unsuccessful due to failure of the mounting flange. The failures occurred adjacent one of the mounting studs and are believed to result primarily from the configuration of the valve body which due to road shock and axle vibration creates certain bending stresses in the mounting flange. The mounting flange is formed integrally with the valve body of a cast white metal or aluminum, both of which are light in weight and economical to manufacture, but they are also relatively brittle and subject to fracture under severe or repetitive bending stresses.
The control valve, in addition to the relay valve mechanism, also supports the override device and may also support the computer and related circuitry. When the latter components are supported in the valve body at a location remote from the mounting flange and the axle is subjected to road shock and vibration, the valve body develops a bending moment relative to the mounting flange which may cause the flange to fracture if stresses of a sufficient magnitude are developed. The potential fracture problem could be avoided by increasing the thickness of the mounting flange. However, this would require a flange having a thickness several times the flange thickness required for vibration free mounting on a vehicle frame or chassis. Such an approach would require either two different valve designs or result in considerable waste of material. The mounting flange style and hole pattern is standardized for replacement purposes. This object would also be defeated if the mounting flange were changed for axle mount units only. The use of a bracket in addition to the mounting flange to secure a portion of the valve body against vibration was also considered. This would require partial disassembly of the valve to secure it to the bracket and the valve would have to be proof tested after it is reassembled and secured to the bracket.
The present invention provides a simple, economical and effective means for mounting a relay valve or control valve directly to an axle and an axle assembly incorporating that means.